Sand cast nickel-base alloy

ABSTRACT

1. AN AIR MELTED, SAND CASTING FORMED OF AN ALLOY CONSISTING OF 20 TO 24% CHROMIUM, 7 TO 11% MOLYBDENUM, 3 TO 4.5% COLUMBIUM, UP TO 0.1% CARBON, UP TO 0.1% ALUMINUM, UP TO LSS THAN 0.0% SILICON, UP TO 12% IRON, UP TO 0.015% BORON, CALCIUM IN A SMALL BUT EFFECTIVE AMOUNT UP TO 0.1% TO IMPROVE REPAIR WELDABILITY, UP TO 0.5% MANGANESE AND 55 TO 62% NICKEL.

United States Patent 3,843,359 SAND CAST NICKEL-BASE ALLOY Michael James Fiene, Ballston Lake, N.Y., and Nathan Lewis Church, Mentor, Ohio, assignors to The International Nickel Company, Inc., New York, N.Y. No Drawing. Filed Mar. 23, 1973, Ser. No. 344,214 Int. Cl. C22c 19/00 U.S. Cl. 75-171 2 Claims ABSTRACT OF THE DISCLOSURE An air meltable, sand casting formed of an alloy containing nickel, chromium, molybdenum, columbium, calcium.

The subject invention is directed to sand casting, and is specially addressed to providing a sand cast counterpart to a well-known commercial nickel-base alloy.

In U.S. Pat. 3,160,500 there is described a matrixstiifened, nickel-base alloy which by virtue of a highly desirable combination of properties, including high stressrupture strength at elevated temperatures, excellent corrosion resistance, good Weldability, etc., has attained a most significant commercial acceptance. As commercially produced, the alloy nominally contains about 61% nickel, 21.5% chromium, 9% molybdenum, 3.65% columbium (plus tantalum), 0.2% each of titanium and aluminum, 2.5% iron, 0.25% each of silicon and manganese and 0.05% carbon and impurities (1). All of its acknowledged attributes notwithstanding, the production of a cast counterpart has left something to be desired. An induction vacuum melted and cast version based upon the conventional nominal alloy chemistry has been advanced (2), and while the proposal has received attention it is inherently costly, a decided drawback.

In any case, it has now been found that an air meltable, sand castable alloy of special and controlled composition aifords an acceptable level of properties together with good castability, the alloy being decidedly less expensive than otherwise might be the case. Moreover, in accordance herewith, problems that too easily could render the conventional alloy unattractive as a sand cast material, e.g., burn on, are also obviated.

Generally speaking, the air meltable, sand castable alloys contemplated herein contain about 20 to 24% chromium, about 7 to 11% molybdenum, about 3 to 4.5% columbium, up to 0.1%, and advantageously not more than 0.05 aluminum, up to 0.1% carbon, up to less than 0.9% silicon, up to 0.5% manganese, up to 12% iron, up to 0.015% boron, and calcium in a small but effective amount, e.g., 0.005%, to afford improved repair Weldability, the balance being essentially nickel.

In carrying the invention into practice, chromium and molybdenum confer both strength and corrosion resistance qualities and in striving for an optimum combination of such characteristics it is preferred that the percentages of these constituents be about 21 to 24% and 8 to respectively. Columbium imparts strength and a range of 3.25 to 4.25% should be maintained. Nickel is preferably maintained over the range of 55 to 62% as in the case of the wrought alloy.

Contrary to the matrix-stiffened wrought alloy, titanium is not deliberately added; indeed, it should be avoided. Furthermore, it is much preferred that any aluminum not exceed 0.04 or 0.05%. It is considered that while these elements would enhance Weldability, they are deemed to detract from surface finish and contribute to burn on problems. This is thought to occur by reaction with the sand mold surface. By avoiding titanium and controlling the percentage of aluminum the castability problems are largely resolved. Weldability difiiculties were encountered.

3,843,359 Patented Oct. 22, 1974 "ice However, it was found that by incorporating and maintaining a small percentage of calcium, e.g., 0.01 or 0.02%, in the alloy possible repair Weldability difliculties would be minimized. In this connection, the upper calcium level should not exceed 0.1%. Apart from the foregoing, the presence of silicon gave an indication of a benefit in terms of Weldability. This element can exceed 0.5%, but it should preferably be controlled to not more than 0.75%.

In order to give those skilled in the art a better appreciation of the invention, the following data are given.

Two air melts (135 kg.) were prepared using an induction furnace (magnesia lined) by first charging electronickel and molybdenum pellets together with Sorel pig. The charge was melted, heated to 2850 F., the carbon boil proceeding to finish. Ferrosilicon was added, the melts then being heated to 2950 F. whereupon Shieldalloy chromium, ferromanganese and ferrocolumbium were added. Aluminum rod was plunged to deoxidize and the melts (three 45 kg. splits of each) were tapped in a ladle at 3000" F. Calcium in the form of a Ni-10 Ca addition agent was added to three of the split heats. No intentional titanium addition was made. The melts were poured (adding ferrosilicon as required) into dry sand molds (one each per split) in the following order: fluidity spirals (2780 F.), Chinese puzzles (2770 F.) and two Keel blocks, one having a 6" x 4" x 4%" leg, the other being 5 /2" x 2%" x 2%". The compositions are given below.

TABLE I Percent.

Fe Cr Mo Cb Al Ca Ni 3.5 21.7 9.1 4.1 0.05 NA Bal. 3.6 21.4 9.2 4.1 0.02 NA Bal. 3.9 21.2 9.1 4.1 0.02 NA Bal. 3.6 21.4 9.1 4.0 0.04 0.017 Bal. 3.6 21.3 9.1 4.1 0.02 0.013 Bal. 8.7 21.2 9.1 4.0 0.02 0.022 Bal.

N orE.--NA=None added.

Essentially of the six sand cast compositions, silicon was varied, i.e., approximately 0.35%, 0.65% and 0.95%, and calcium was added to three splits; otherwise, the compositions were virtually the same.

No difliculties were experienced in air melting and the sand castings were of good surface appearance at all three silicon levels and both with and without calcium. Silicon did not improve the surface finish of the Chinese puzzles and seemed to decrease the length of the fluidity spirals. Calcium did not aid castability, slight cold shutting being noted on the Chinese puzzles. Given that Chinese puzzles serve as a good indication of the propensity of an alloy to form cold shuts or to react. with a mold and that the length of a fluidity spiral provides a good indicia as to fluidity and thus the ability to fill a mold cavity, overall castability was considered as very satisfactory.

Tensile properties, repair Weldability characteristics and corrosion resistant capabilities of the heats were also assessed. Tensile specimens were cut from the first given Keel leg, the tests being conducted in both the as-cast and heat treated conditions (1 hour at 2050" F. followed by water quenching).

TABLE II .As-cast 1 hr./2,050 FJWQ EL, RA, EL, RA, ofiset, UTS, perperoffset, UTS, perper- Alloy p.s.l. p.s.i. cent cent p.s.l. p.s.i. cent cent 40 34.5 43,000 76,600 37 32 18.5 17 42,600 72,900 29.5 31 9 12 ,400 74,100 21 25.5 36.5 31 41,200 67,400 29.5 22 16.5 14 42,200 71,700 25.5 24 14 14 42,500 71,200 19.5 22

Norm-All results are averages of two tests.

In an effort to determine probable repair weldability behavior, as-cast blocks with machined grooves were filled with a commercially available welding electrode used in welding the alloy of US. Pat. No. 3,160,500, the electrode containing about 61% Ni, 21.5% Cr, 9% Mo, 3.65%

conjunction with preferred embodiments, modifications may be resorted to. For example, while titanium is to be avoided, a minor level, say, up to 0.02 or 0.03% might be tolerated. Tantalum to the extent associated with columbium can be present. Such modifications are con- Cb-l-Ta, 4% Fe, 0.3% Mn, 0.05% C, and 0.4% Sr plus srdered to be within the purview and scope of the invenimpurities. Each weldment was sliced into six sections tion and appended claims unless indicated to the contrary.

transverse to the weld bead and the cast faces were We claim: polished, etched and examined for cracks at a mag- 1. An air melted, sand casting formed of an alloy connification. The results are reported in Table III. Included 10 sisting of to 24% chromium, 7 to 11% molybdenum, are the silicon and calcium levels. 3 to 4.5% columbium, up to 0.1% carbon, up to 0.1%

TABLE III Slice and face number Percent 2 3 4 5 Cracks/ Total face Alloy Si Ca 1 A B A B A B A B 6 cracks examined 1 0.31 a 1 1 OK OK 2 OK 1 OK OK 3 0.8 2 0.65 4 1 1 OK 1 1 1 1 OK 1 11 1.1 3 0.98 OK OK OK 1 OK OK OK OK OK 1 2 0.2 1 OK OK OK X x OK 1 OK OK 2 0.25 5 OK OK OK OK OK OK OK OK 1 OK 1 0.1 0K OK OK 0K OK OK OK 0K OK OK 0 0 N OTE.OK=N0 cracks observed. X=Not examined. The cracks varied from 0.02 to 0.06 in length.

No cracking of the weld metal was observed, all the cracks occurring outside the deposit. Silicon seemingly enhanced weldability as reflected by a decrease in the number of cracks. This is deemed so unusual as to bear confirmation. In any event, calcium was decidedly beneficial and is deemed of marked benefit for repair welding.

Concerning the corrosion test, specimens of the second Keel block above described, either as-cast or heat treated (1 hr. at 2050 F. and air cooled), were immersed in 10% ferric chloride (180 g./l. FeC1 -6H O) maintained at room temperature, the test covering a 72-hour period. A rubber band was used to form a crevice. None of the six alloys exhibited any significant Weight loss or visible sign of attack, notwithstanding the severity of the test.

The sand cast alloys contemplated herein are generally useful where a high degree of corrosion resistance, notably in chloride type environments, is desired coupled with a good level of mechanical characteristics. The alloys are particularly useful in marine hardware applications such as cast fittings for use in seawater.

Although the present invention has been described in UNITED STATES PATENTS 3,160,500 12/1964 Eiselstein et al. 171

OTHER REFERENCES Huntington Alloys Handbook, 1970 edition, p. 5, published by The International Nickel Company, Inc.

Tensile and Stress-Rupture Properties of Cast Alloy 625, published by The International Nickel Company, Inc., (1969).

RICHARD O. DEAN, Primary Examiner 

1. AN AIR MELTED, SAND CASTING FORMED OF AN ALLOY CONSISTING OF 20 TO 24% CHROMIUM, 7 TO 11% MOLYBDENUM, 3 TO 4.5% COLUMBIUM, UP TO 0.1% CARBON, UP TO 0.1% ALUMINUM, UP TO LSS THAN 0.0% SILICON, UP TO 12% IRON, UP TO 0.015% BORON, CALCIUM IN A SMALL BUT EFFECTIVE AMOUNT UP TO 0.1% TO IMPROVE REPAIR WELDABILITY, UP TO 0.5% MANGANESE AND 55 TO 62% NICKEL. 